The Session Initiation Protocol (SIP) is a general-purpose signaling protocol used to control media sessions of all kinds, such as voice, video, instant messaging, and presence. SIP is a protocol of growing importance, with uses in Voice over Internet Protocol (VoIP), Instant Messaging (IM), IP Television (IPTV), Voice Conferencing, and Video Conferencing. Wireless providers are standardizing on SIP as the basis for the IP Multimedia System (IMS) standard for the Third Generation Partnership Project (3GPP). Third-party VoIP providers use SIP (e.g., Vonage), as do digital voice offerings from existing legacy Telcos (e.g., AT&T, Verizon) as well as their cable competitors (e.g., Comcast, Time-Warner).
While individual servers may be able to support hundreds or even thousands of users, large-scale Internet Service Providers (ISPs) need to support customers in the millions. A central component to providing any large-scale service is the ability to scale that service with increasing load and customer demands. A frequent mechanism to scale a service is to use some form of a load-balancing dispatcher that distributes requests across a cluster of servers.
However, almost all research in this space has been in the context of either the Web (e.g., HyperText Transfer Protocol or HTTP) or file service (e.g., Network File Service or NFS). Hence, there is a need for new methods for load balancing techniques which are well suited to SIP and other Internet telephony protocols.